Impeller



Sept 22, 1964 R. A. ENTRIKIN 3,149,823

IMPELLER Filed Feb. 1e, 1962 1'an...1....Ip-.-.--Ill'aa'l'll...11.4.

31E 5 INVENTOR.

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United States Patent O 3,149,823 IlVPELLER Raymond A. Entrikin, East Liverpool, Ohio, assigner t Patterson Industries, Inc., a corporation of @ino Filed Feb. 16, 1962, Ser. No. 173,681 9 Claims. (Cl. 259-134) This invention relates to an impeller and more particularly 'to the type of impellers used to disperse granular or powdered solids into a liquid in a mixing vessel. Specific-ally, the type of impeller described herein h-as been found useful for mixing paints, enamels and like substances. However, it will be apparent .to those skilled in the .art that the type of impeller described below is useful for a variety of mixing :or stir-ring appplications.

Impellers used for mix-ing paints conventionally have blades arranged as an -air screw for drawing the liquid toward and through the impeller. The rotating blades in conventional impellers cause the mixture to rotate in a circular direction, so that a considerable portion `of the mixture is not agitated, b-ut merely swirls around the periphery of the mixing vessel. This is generally known as an excessive vortex problem, since the `swirling mixture is evidenced by a vortex in the center of the vessel. In the past, numerous attempts have been made to vary the proiile of the impeller blades so that the impeller may still act a-s an air screw pump and at the same time minimize the vortex problem.

An object of this invention is to minimize the vortex problem by utilizing a turbine pump principle rather than an air screw principle in the construct-ion and operation of an impeller.

Another troublesome problem is encountered when it is desired to disperse powdered or granulated substances into a liquid, suc-h as when pigments are mixed ina paint Normally, pigments and other powdered or granulated materials are easily wetted and disperse freely in a liquid mixture, so long as the surfaces of the powdered or granulated material are exposed to the liquid. As well known, however, powdered or granulated materials rsuch as pigments often form small bundles covered by a film of liquid, which are known as agglomerates. Since the individual particles forming the .agglomerates are not wetted, agglomerates do not readily 4disperse within the liquid.

A further object of this invention is to provide an impeller especially adapted to aid in breaking up agglomerates, whereupon the particles forming in the agglomerates are readily wetted and dispersed in the liquid mixture.

Other `objects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode yof operation, as will become more apparent from the following description.

Referring yto the drawing, FIGURE l is a perspective View of an impeller made in accordance with this invention.

FIGURE 2 is an elevational view of lthe impeller of FIGURE l mounted upon a shaft showing the impeller submerged in a liquid mixture in a mixing vessel and diagrammatically illustrating the paths of the mixture ow created upon rotation of the impeller.

FIGURE 3 is a sectional view of the mixing vessel taken along line 3 3 of FIGURE 2, and shows the impeller in plan view.

FIGURE 4 -i-s a View similar to FIGURE 3 showing a slightly modified form of impeller made in accordance with this invention.

FIGURE 5 is an elevational view similar to FIGURE 2 showing the modified impeller of FIGURE 4 as viewed in the direction of the line 5-5 in FIGURE 4.

In FIGURES 2 through 5, the sizes of the impellers are greatly enlarged relative to the mixing vessels illustrated therein in order to fully disclose the impeller structure.

Referring in greater `detail to FIGURES l, 2 and 3 of the drawing, an impeller generally designated 10 is shown therein as comprising three identical larcuate vanes 12 encircling a hub 14 connected to a rotatable impeller 4shaft 16 for rotation therewith. As indicated by the arrow A in FIGURE 3, suitable means (not shown) are provided to rotate the shaft 16 and, accordingly, the impeller 1t) in a clockwise direction as viewed in FIG- URE 3.

Each of the vanes 12 comprises a thin strip of material having parallel inner and outer faces 20 and 22 respectively. Each vane 12 and, accordingly, the faces 20 land 22, terminate in edges which, based upon the direction of rotation, are conventionally known as a leading edge 24 and a trailing edge 26. The faces 20 and 22 are parallel throughout substantially their entire length Iand are parallel at each point thereon to the axis of rotation of the shaft 16. At the trailing edge 26 :the inner face 20 diverges from the outer face 22 so that each vane 1.2 is slightly thicker at its trailing edge 26 than vthroughout the rest of its length. Since three vanes 12 are shown in FIGURES l, 2 and 3, each extends through an arc of substantially and the vanes 12 are so spaced that the trailing edge 26 of one vane 12 terminates on the same radial line on which the leading edge 24 of an adjacent vane 12 begins.

rPhe longitudinal center lines o-f the three vanes 12 are coplanar. Accordingly, the three vanes 12 may be mounted on a single flat plate Si? connected to the hub 14 such that Ithe vanes 12 are perpendicular to the plate 30, which conventionally occupies a horizontal position when in use. The plate 30 is formed with three blade portions 38a, 30b rand 30C having outer peripheries matching the contour of the inner faces 20 of the vanes 12. Each of the blade portions terminates in a radially projecting edge .31 extending between the leading edge 24 of one vane 12 and the trailing edge 26 of an adjacent vane 12.

It is desired that clockwise rotation of the vanes 12 creates a primarily radially outward ow of the liquid mixture as viewed in the direction of the arrows B in FiGURE 3. To this end, the leading edges 24 are radially cioser to the axis of rotation of the shaft 16 than the trailing edges 26, yet there is a definite radial spacing between the leading edges 24 and the axis of rotation. Each of the vanes 12 is curved along its length to form an arc having a gradually increasing radial distance from the center of rotation. The arc formed by the vanes 12 is such that the tangent to any selected point on the vane surface lies at an angie of less than 15 to the normal to the radial line projecting from the axis of rotation at that point. Best results are achieved when the angle defined above, which is called the discharge angle at the trailing edges 26, is between 8 and 15. Although a vane having such a configuration causes a small amount of swirl, the flow is primarily radially outwardly from the axis of rotation.

As indicated by the arrows C in FIGURE 2, the liquid mixture, designated 32, moving radially from the outer faces 22 of the vanes 12 is split into two paths at the wall of the mixing vessel, designated 34, thus forming an upward path :and a downward path of mixture along the wall of the vessel 34. The impeller lll acts as a turbine pump since the radially outward flow of the liquid mixture 32 creates a low pressure area along the horizontal plane of the plate 3i). Accordingly, the mixture flowing upwardly and downwardly along the wall of the vessel dd is drawn back 'to the plane of the impeller 10 whereupon two generally circular paths cf liquid flow are created within the vessel 34, one above and one below the plate 30, as diagrammatically illustrated in FIGURE 2. rl`hus, although the swirling of the liquid is kept to a minimum by utilizing a turbine principle rather than an air screw principle, liquid mixture from all portions of the vessel is continuously liowinfT first laway from the impellcr bt) to the wall of the vessel 3d and tiren back toward the center of the impeller So that all portions of the outer faces 22 of the vanes 12 are eiiicient to propel approximately the same amount of mixture radially outwardly, the widths of faces 20 and 22 taper along their length from a maximum at the leading edges 24 to a minimum at the trailing edges 26. Since the leading edges 24 are radially closer to the axis of rotation, their angular velocity will be less than that of the trailing edges 26. Accordingly, the leading edges must be wider than the trailing edges 2o so that all portions of the outer faces 22 propel the same mass of liquid mixture in any given interval of time.

Dispersion of the agglomeraties is accomplished in accordance with this invention partly by the shear forces created within the liquid mixture and the wiping action of the liquid mixture along the surface of the vanes l2. A liquid mixture shears when it is subjected to a rapid change in direction or velocity. The liquid mixture 3i?. is sheared at the surface of the vanes l2 since portions of the mixture flow slowly vertically toward the impeller lil, strike the vanes l2, and move rapidly radially outwardly in a horizontal plane toward the wall of the vessel 3d. Of course, the liquid mixture 3.. is again subjected to shear forces as it is split into two paths near the vessel wall.

It is believed that a more important factor in breaking up the agglomeraties is the cavitation that necessarily will result due to the abrupt changes in the inipeller faces 22 along the radial lines common to adjacent vanes. The impeller lil would be va more efficient turbine blade if the trailing edges 26 were narrowed to a feather edge. rhis is normally done in turbine pumps to avoid cavitation. However, in accordance with this invention, the trailing edges 26 yare thickened to magnify the cavitation which would ordinarily occur at these edges upon rotation of the impeller. Cavitation areas are areas of turbulence having an extreme low pressure. Because of the low pressure, the agglomerates are drawn into the cavitation area. Any gases within the agglomerates will expand, causing the agglomerates to burst or break up so that the particles forming the agglomerates are exposed to the liquid and thoroughly wetted. Dispersion of the particles including agglomerates due to the cavitation, coupled with the dispersion due to the ordinary wiping and shear forces, has been found most effective to thoroughly disperse solids within a liquid mixture in a very short time.

Referring now to FIGURES l and 5, a modified impeller I@ is shown therein. However, like reference characters are applied to like parts. The only difference between the impeller it? shown in FIGURES 4 and 5 and that shown in FIGURES l, 2 and 3 is that the number of vanes 12 has been increased from three to four. As apparent, each of the vanes l2 has a length of 99 rather than 120. Again, each of the vanes l2 are mounted upon a flat plate 3d which is connected to a hub le and in turn to a shaft lo. In this case, the plate 39 has four blade portions, designated 39a, 3%, Stic and Stia. As bew fore, when using four vanes I2, it is desirable to provide a thickened trailing edge 2d to increase cavitation effects. The arrows C in FIGURE indicate that the general flow created by four vanes l2 is the same as in the three vane structure shown in FIGURES l, 2 and 3. To this end, the discharge angle of the vanes il?. used in the device of FIGURE 4 again lies between 8 and 15. rIhe four Vane structure is used for larger impellers than the three vane structure. For example, a satisfactory sixinch diameter impeller has been made with three vanes while a twelve-inch impeiler has been made with four l vanes. Further description is believed unnecessary since the impeller shown in FIGURES 4 and 5 is otherwise identical to that described above in relation to FIGURES l, 2 and 3.

Among other advantages, the constructions described above provide a thorough mixing of the mixture 32 throughout the vessel 3d. Since the vanes 12 are symmetrical about their longitudinal center lines and, therefore, the plate 3d, mixing occurs both above and below the plate Sti. Many impeller constructions create excessive splashing caused by the impact of the rotating blades or vanes with the moving or swirling liquid. Because of the low discharge angle employed in the instant construction, splashing is kept to a minimum.

rl`he impellers described above may be cast in one operation. Alternatively, the parts can be made separately and welded together. When welded, the thickened edges 26 may be formed separately from the remainder of vanes l2 and welded thereto.

Although the presently preferred embodiment of the device has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

l. An impeller of the type adapted to be placed in a mixing vessel for dispersing particulate solids into liquids contained in the vessel, said impeller comprising: a plate having a flat surface and adapted to be attached to an impeller shaft for rotation about a predetermined axis normal to said surface; and a plurality of substantially identical vanes, each of said vanes comprising a thin strip connected to the periphery of said plate perpendicular to said fiat surface, said strip having a leading edge and a trailing edge, the leadiuU edge being radially closer to the axis of rotation of the plate than the trailing edge, the radially outermost surface of said strip intermediate its leading and trailing edges forming an arc having a continuously increasing radius, and said thin strip having a thickened trailing edge to increase cavitation at the trailing edge.

2. The impeller of claim l wherein each of said strips has generally coextensive radially inner and outer surfaces tapering from. a maximum width at their leading edges to a minimum width at their trailing edges.

3. The impeller of claim l wherein the vanes are connected along their longitudinal center lines to the periphery of the plate.

4. An impeller of the type adapted to be placed in a mixing vessel for dispersing particulate solids into liquids contained in the vessel, said impeller comprising: a plate having a dat surface and adapted to be attached to an impeller shaft for rotation about a predetermined axis normal to said surface, a plurality of vanes connected to the periphery of said plate perpendicular to said flat surface, each of said vanes having a leading edge and a trailing edge, the leading edges being radially closer to the axis of rotation of said plate than the trailing edges, the radially outermost surfaces of each of said vanes intermediate its leading and trailing edges forming an arc having .a continuously increasing radius, and said vanes having a discharge angle between 8 and 15.

5. An impeller of the type adapted to be placed in a mixing vessel for dispersing particulate solids into liquids contained in the vessel, said impeller comprising: a plurality of vanes and means for connecting said vanes to an impeller shaft for rotation therewith, each of said vanes having closely spaced inner and outer arcuate surfaces so connected to said shaft as to be parallel thereto, said surfaces being mutually parallel throughout substantially the entire lengths thereof and terminating in a leading edge and a trailing edge, said leading edge being closer 'fi to the axis of rotation of said shaft than said trailing edge, said surfaces diverging at said trailing edge to increase the cavitation in a liquid in which the impeller is submerged While the impeller is rotating.

6. The irnpeller of claim 5 wherein each 0f the vanes forms an arc having a gradually increasing radius from the leading edge thereof to the trailing edge thereof, the discharge angle of said Vanes being between 8 and 15.

7. The impeller of claim 5 wherein the means for connecting the vanes to said shaft includes a at plate, said vanes being connected along their longitudinal center lines to the periphery of said plate.

8. The impeller of claim 7 wherein the widths of said surfaces taper along the lengths thereof from a maximum at their leading edges to a minimum at their trailing edges.

9. An impeiler of the type adapted to be placed in a mixing vessel for dispersing particulate solids into liquids contained in the vessel, `said impeller comprising: a plurality of vanes, each of said vanes having closely spaced inner and outer arcuate surfaces, said surfaces terminating in a leading edge and a trailing edge and diverging from one another at said trailing edge; and means connesting said vanes to an impeller shaft for rotation therewith about a predetermined axis with said surfaces perpendicular to a plane normal to said axis, with said blades circumferentially spaced about said axis, and with said leading edges of said vanes being closer to said axis than 10 `said trailing edges.

References Cited in the tile of this patent UNITED STATES PATENTS 2,418,547 Cowles Apr. 8, 1947 FOREIGN PATENTS 148,643 Switzerland Oct. 1, 1931 578,525 Canada June 30, 1959 858,112 Great Britain Jan. 4, 1961 

5. AN IMPELLER OF THE TYPE ADAPTED TO BE PLACED IN A MIXING VESSEL FOR DISPERSING PARTICULATE SOLIDS INTO LIQUIDS CONTAINED IN THE VESSEL, SAID IMPELLER COMPRISING: A PLURALITY OF VANES AND MEANS FOR CONNECTING SAID VANES TO AN IMPELLER SHAFT FOR ROTATION THEREWITH, EACH OF SAID VANES HAVING CLOSELY SPACED INNER AND OUTER ARCUATE SURFACES SO CONNECTED TO SAID SHAFT AS TO BE PARALLEL THERETO, SAID SURFACES BEING MUTUALLY PARALLEL THROUGHOUT SUBSTANTIALLY THE ENTIRE LENGTHS THEREOF AND TERMINATING IN A LEADING EDGE AND A TRAILING EDGE, SAID LEADING EDGE BEING CLOSER TO THE AXIS OF ROTATION OF SAID SHAFT THAN SAID TRAILING EDGE, SAID SURFACES DIVERGING AT SAID TRAILING EDGE TO INCREASE THE CAVITATION IN A LIQUID IN WHICH THE IMPELLER IS SUBMERGED WHILE THE IMPELLER IS ROTATING. 